Someone who is not medically mentally handicapped, but some of their actions make you wonder what their mental capacity is. Often this person will do something stupid, and not realize it was stupid until others point it out to them. A re re is noticeable in the crowd because people are often pointing and laughing.

She was so busy texting while she was driving, that she didn't see the car in front of her and she rear ended it. She's such a re re!
She was soo drunk, that she peed her pants! She's a definite re re!
Quentin got so drunk that he passed out and got colored on all over his body with a permanant marker - he looked like a re re!